Method of increasing the strength of hollow metal articles



Sept. 8. 1925.

F."C. LANGENBERG METHOD OF INCREASING THE STRENGTH OFHOLLOW METALARTIGLES Filed March 28, 1925 MAGHINELD liq- 1 FmaT EXPANKNNG 3 ECOND EXPAN DING H n F1 HFH-fl 5 V .4mm l- @THIRD EXPANDING- MM 5% P 4 NTERNAL PREEnSURl FuRsT ANNEALING jgconn AuuzAuNG z A NNEAL BORE. LNLARG-EME-NT I VEN+EIV Z Patented- Sept. 8, 1 925.

4 UNITED STATES-PATENT OFFICE.

rnnnnnicx o. LANGENBERG, or CAMBRIDGE, unssacnusm'rs, AssIqnoR or ONE- HALF TO TRACY C. DICKSON, O1 WATERTOWN;MASSAGHUSETTS..

METHOD OF INCREASING THE STRENGTH' OF HOLLOW METAL ARTICLES.

Application filed. March 28, 1825. Serial 1T0. 18,178.

it has been known that if a hollow steel arti do is expanded or stretched beyond its elastic limit the elastic limit will be pern-ianently raised.- Attempts have been made to apply this principle to the manufacture of guns but no considerable commercialsuccess has been attained because it has been impossible to control the increase in elastic limit in an article of varying thickness. plieation tiled March 28, 1995, Serial No. 19001 I have disclosed a method and app'a ratus by which it is possible to raise the clastion a predetermined amount and to whatever extent is required. In practicing this method in connection with the manufacture of guns and shells, I have made certain discoveries which greatly increase the possibilities of usefulness of the method of increasing the elastic limit of hollow metal artieles which consists in subjecting them to .an internal expanding pressure.

I have discovered that for a given percentage ofenlargeinent. over the original size of the article, a greater increase in elastic limit takes place if the enlarging is done in successive steps and the article is annealed and cooled between the successive stretching steps. Accordingly in the manui'acture of certain articles it is desirable to subject the articlevto successive expansion treatments alternating with annealings. M novel method herein described therefore makes it possible to increase the strength ofa given material or to use an inferior mate'- rial for an article requiring a given strength. My improved method is also efi'cctively practice'd in conjunction with another novel method described in a companion application filed March 28, 1925, Serial No. 1917 2 in which the manufacture of guns and shells s de b d- In an aptic limit of an article of non-uniform sec-.

direct from the casting and without forging The invention .will be fully understood from the following description'when taken in connection with the accompanying drawings and.-. the novel features thereof will be pointed out and clearly defined in the claim at the close of this specification.

, In the drawin s:

Fig. 1 shows the article after it has been machined.

Fig. 2 illustrates the, first expanding step. Fig. 3 shows the first annealing step. Fig. 4 illustrates the second expanding step.

Fig. 5 shows the second annealing step. Fig. 6 illustrates the third expanding step. Fig. 7 isa diagram showing the effect on the elastic limit of the article.

In practicing my improved invention I proceed as follows: The hollow article A is preferably machined on the surfaces required as indicated at B. It is then placed 7 (see Fig. 2) in a container 0 and expanded a predetermined amount which amount is determined by the shape of the interior of the container, then it is removed from the container'and annealed as indicated in Fig. i

3 in the furnace D. After being allowed to cool, it is placed in a second container E (see Fig.4) and again expanded. After being expanded it may be again annealed, as shown in Fig. 5 and thenagain expanded in the container F, Fig. 6.

The effect onthe elastic limitor strength of the article is indicated in the diagram shown in Fig. 7. In this diagram per cent of enlargement is plotted against the interior pressure. producin the enlargement. resulting curves s ow the chan es in the elastic limit. Theccurve P shows t e changes in elastic limit or a iece which is notannealed. The curve shows the change for a piece which is annealed twice at M and What I claim is:

The method of increasing the strength of metals which consists in subjecting the article to an interifal expanding pressure restrained to prevent its passing beyond a predetermined point, annealing the article and again subjecting it to a restrained expansion.

In testimony whereof I aflix. my signature.

FREDERICK .0. LANGENBERG,

The" 

